Electronic apparatus and method

ABSTRACT

An apparatus for and method of causing the concentration of coating materials in a coating solution to be automatically adjusted. The apparatus monitors the current flow from a power source to the coating solution and provides pulses substantially proportional to the integral of such current flow. The apparatus counts in a first direction in response to the pulses and energizes means causing the coating material solution to be adjusted in response to counting in the first direction. The energized means causing counting in a second direction until the apparatus reaches a determined count at which time the adjustment of the coating material is terminated.

Unite States atom [72] Inventors George G- GOI OII; 3,305,467 2/1967 lgras et al. 204/181 Donald E. Orem, both of Indianapolis, Ind. 3,418,225 12/1968 Wick et a1 204/181 [21] Appl. No. 798,935 3,502,563 3/1970 Schmidt 204/181 [22] Filed Feb. 13,1969 3,475,316 10/1969 De Vittorio 204/181 [45] Patented Dec. 14, 1971 [73] Assignee Ransburg Electro-Coatlng Corp. Pnmary Examme.r Howal-d wllhams Indiana 8 Ind Attorneys-Merrill N. Johnson, Harry E. Downer, David H.

Po Badger and Charles W. Hoffman [54] ELECTRONIC APPARATUS AND METHOD 14 Claims3Drawing Figs ABSTRACT. An apparatus for and method of causing the concentrat1on of coating materials m a coating solution to be [52] U.S.Cl 204/181, automatically adjusted. The apparatus monitors the current 2 4/300 flow from a power source to the coating solution and provides [51] Int. Cl BOlk 5/02 pulses substantially proportional to the integral of such cur- [50] Fleld oi Search 204/181, rent flow. The apparatus counts in a first direction in response 300 to the pulses and energizes means causing the coating material solution to be adjusted in response to counting in the first [56] Rflerences Chad direction. The energized means causing counting in a second UNITED STATES PATENTS direction until the apparatus reaches a determined count at 3,355,373 11/1967 Brewer et al 204/181 which time the adjustment of the coating material is minated.

Tb CATHODE ELECTRODE 7/ 20 29 3o 31 I l LINEAR PR T I INTEGRATOR ESE I I 2 COUNTER I POWER I CONTROL I UNIT I To I PREMIX I I TANK 2 I 3 33 I I8 11c. I REVERSIBLE TIMER SUPPLY I COUNTER I I 21 L I COATING MATERIAL J SUPPLY MEANS 27 PATENTEUnmmsm 3,627, 1

sum 1 0F 3 ELECTRONIC DEVICE l9 POWER CONTROL UNIT SUPPLY Fig.

INVENTOR GEORGE G. GORDON DONALD E. OREM The present invention relates to an apparatus for and to a method of adjusting the concentration of a coating solution used to electrophoretically deposit a coating material upon an electrically conductive substrate. More particularly, the present invention relates to an electronic means for regulating the actuation of a means capable of causing the flow of the coating material from a coating material reservoir to a coating solution to thereby automatically control, within desired concentration limits, the concentration of the coating material in the coating solution.

The application of a direct current to a pair of electrodes immersed in coating solution which includes a suspension of colloidal particles dispersed in a fluid medium of relatively high dielectric constant causes an electrochemical reaction to occur. The electrochemical reaction involves the migration of the colloidal particles under the influence of an electric field in a fluid medium. The electrochemical reaction is known as electrophoresis. During the electrophoretic deposition process, the suspended colloidal particles are attracted to and tend to adhere to the immersed electrode having a polarity opposite to the polarity of the colloidal particles.

A vessel of electrically conductive material may be made the cathode electrode and the conductive substrate to be coated by the coating solution within the vessel may be made the anode electrode. In addition, the vessel may be fabricated from a suitably insulative material and a cathode electrode may be immersed in the coating solution with the conductive substrate made the anode. Current for the system is supplied by a suitable direct current (DC) source. The coating solution usually includes a coating material such as suspended particles of pigments, resins and the like which carry a predominately negative charge. The negatively charged particles of the coating material are attracted to the immersed positively charged conductive substrate. Upon contact with the conductive substrate, the charge carried by the substantially removed and the particles of coating material tend to coagulate on the conductive substrate. The electrophoretic deposition of the coating material onto the immersed substrate continues until a coherent, substantially uniform film of coating material covers the substrate.

Electrophoresis is possible with a myriad of coating materials including solid resins, emulsions, macromolecular solutions and the like. The choice of the coating material to be used to coat the substrate appears to have an influence on the thickness of the film of coating material which may be deposited on the substrate, the quality of surface finish of the film of coating material, the ability of the coating material to deposit sharp corners of the substrate and the like. Generally, emulsions and colloidal suspensions coat the substrate more rapidly than several of the other types of coating materials but appear to have limitations when used to coat substrates having sharp comers or edges.

Other factors which may influence the electrophoretic deposition process include, but are not limited to, the electrical characteristics of the direct current power supply, the length of time the conductive substrate is immersed in the coating solution with current flowing thereto from the direct current source, the geometry of the substrate, the type and extent of pretreatment experienced by the surfaces of the substrate prior to being immersed in the coating solution, the concentration of the coating material in the coating solution, the current density and the like. If any of the several abovementioned factors vary, the quality and thickness of the coating material film deposited onto the substrate may vary widely. For example, if the current density varies, the amount of material deposited upon the substrate per unit of time will vary; if the concentration of the coating material drops below a minimum concentration, the amount of coating material deposited onto the substrate may not be sumcient to properly coat the substrate in the length of time the substrate is immersed in the coating solution. Therefore, an unwarranted amount of operator supervision is required during'the electrophoretic deposition process in order to insure that the concentration of the coating materials in the coating solution are not depleted below a level which is necessary to achieve a satisfactory deposition of the coating material upon the substrate.

Therefore, it is the object of the present invention to provide an apparatus and a method for overcoming the abovementioned problems.

Another object of the present invention is to provide an apparatus which substantially automatically adjusts the concentration of some of the constituents of a coating solution during the coating operation of substrates by adding constituents to the coating solution.

A further object of the present invention is to provide an apparatus which adjusts the concentration of a coating solution that requires less operator supervision than required by several of the prior art devices.

Another object of the present invention is to provide an electronic apparatus which adjusts the concentration of a coating solution.

Yet another object of the present invention is to provide an electronic apparatus which causes adjustment of the concentration of a coating solution that reacts to the rate at which the coating material of the coating solution is depleted therefrom.

A further object of the present invention is to provide a method for adjusting the concentration of the constituents of a coating solution.

Another object of the present invention is to provide an electronic apparatus which causes adjustment of the concentration of a coating solution that is sensitive to the rate of deposition of the coating materials per unit of time.

Yet another object of the present invention is to provide an electronic apparatus which causes adjustment of the concentration of a coating solution used in an electrophoretic deposition process.

A further object of the present invention is to provide an electronic apparatus which causes adjustment of the concentration of an electrophoretic coating solution that is economical to construct and inexpensive to operate.

With the aforementioned objects enumerated, other objects will be apparent from reading the following description and the appended claims.

In the drawings:

FIG. 1 is a partially schematic, partially sectional side view of an electrophoretic apparatus illustrating use of the present invention with the apparatus;

FIG. 2 is an electrical block diagram showing the apparatus for adjusting the concentration of a coating solution; and

FIG. 3 is an electrical schematic illustrating one flip-flop means of a plurality of cascaded flip-flop means used in the preset counter illustrated in FIG. 2.

Generally speaking, the present invention relates to an apparatus and to a method for adjusting the concentration of the coating materials in a coating solution. The coating solution includes a coating material to be electrocoated upon an electrically conductive substrate while the substrate is passing through the solution. The apparatus includes a first means for monitoring the current flow from a direct current (DC) power source to the coating solution. The first means is capable of providing output pulses proportional to the current flow from the power source to the coating solution. The first means may include a shunt means, a linear amplifier and an integrator connected in series combination. A second means is connected to the first means and is capable of providing an output pulse when the output pulses of the second means exceed a predetermined count. The second means may include a preset counter A third means is connected to the second means and is capable of counting in a first direction when the output pulses of the second means are impressed thereon. The third means may include a reversible counter. A fourth means is connected to the third means. The third means is capable of causing actuation of the fourth means when the third means is counting in the first direction. The fourth means is capable of providing a pulse to the third means which causes the third means to count in the direction opposite to the direction of the output pulses of the second means. The fourth means is deactuated when the count of the third means is a predetermined count. The actuated fourth means is capable of actuating a coating material pump which, in turn, is capable of causing a coating material to be introduced into a coating tank thereby adjusting the concentration of the coating material in the coating solution. The fourth means may include a programing device such as a cam timer and the like.

Referring now to FIG. 1 of the drawing, a plurality of conductive substrates l such as appliance housings, automobile horns, aluminum extrusions for window frames and the like may be suspended from a suitable conveyor means ill by any suitable hanger mechanism 12. It is understood that the conveyor means may have substituted therefor a suitable batch processing apparatus. The conductive substrate it) may be fabricated from iron, steel, copper, zinc, brass, tin, nickel, chromium, aluminum and the like. The conveyor means 11 may include a conveyor track 60 and a suitable hanger drive means (not shown) which may be used to transport the conductive substrates it) along a path determined by the configuration of the track of the conveyor means. The hanger mechanism 12 may include a plurality of wheels 50, suspension means connected to the wheels 50, an insulative means 13 connected to the suspension means 51 and a contact plate M connected to insulative means 13. Connection of the contact plate 14 between the conductive substrate and the insulative portion 13 of the hanger serves to electrically insulate the contact 14 from the conveyor means lll so that the conveyor means does not serve as a conduit for current flow. The insulative means 13 may be fabricated from any suitable nonconductive material of good strength such as polytetrafluoroethylene and the like. The contact plate 14 may be fabricated from any suitable electrically conductive, noncorrosive metallic material such as stainless steel and the like.

The conductive substrates 10 are transported along the path determined by the configuration of the conveyor track of the conveyor means 11 to a vessel or tank l6 containing a suitable coating solution 15. The coating solution may include a suitable coating material of negatively charged resins and pigments to be deposited on the charged substrates ll) during the length of time each of the charged substrates is immersed in the coating solution. The tank 16 may be fabricated from any suitable noncorrosive, electrically conductive material such as stainless steel or the like. The tank 16 may be connected to the negative terminal of direct current (DC) power supply 18 by any suitable conduit such as copper wire or the like. When the tank 16 is connected to the negative terminal of the power supply 18, the tank serves as the cathode electrode during the electrophoretic deposition process.

Bus bar 17 is suitably positioned adjacent the conveyor means ill and adjacent the rim of the tank 16 in such a manner that the contact plate 14 of each hanger mechanism 12 engages with the bus bar 17 during the length of time each of the substrates 10 is immersed in the coating solution 15. The bus bar 17 is shown in H6. 1 as being connected to the positive terminal of the DC power supply 18. Therefore, the bus bar 17 is an anode bus bar. Each substrate 10 is positively charged during the length of time the contact plate M of the hanger mechanism is in contact with the anode bus bar. The suspended particles of the coating material such as negatively charged particles of resins and pigments are attracted to and deposited on each positively charged substrate 10 immersed in the coating solution. The deposited particles tend to coagulate on each substrate. The electrophoretic process continues until a substantially uniform film of coating material covers the metal surfaces of the substrate 10.

in another embodiment, the conveyor means ll may be grounded thereby eliminating the insulative means 12 and the means used to electrically connect the substrates ill to the positive terminal of the DC power supply 18 such as bus bar 17 and the like. In the embodiment, the cathode electrode is separate from the tank 16. Tank 16 is grounded. The cathode electrode is immersed in the coating solution and is connected to the negative terminal of the power supply 18. The substrates w are directly connected to the conveyor means 11, that is, the insulative means 12 is eliminated, and the conveyor means is connected to ground and the positive terminal of the power supply 18.

Although not absolutely necessary, in a batch type processing apparatus, it may be desirable to provide a power control unit 19 between the DC power supply 18 and the anode and the cathode electrodes. The power control unit 19 is capable of increasing the voltage applied to the anode electrode or bus bar 17 as the resistivity of the anode 10 increased due to the deposition of the coating materials thereon from the solution. The application of an increased voltage to the anode electrode counteracts the increasing resistivity of the anode and results in substantially constant current density.

Generally, the coating material deposited on each conductive substrate cannot be removed by washing the coated substrate with water immediately after removing the coated substrate from the coating solution. it should be seen that the electrophoretic method of depositing a coating material onto the conductive substrates 10 includes all the advantages of dipping and additional advantage of providing a thin, substantially uniform deposit of coating material free of retained solvents thereby resulting in a paint coat savings over a standard dipping process. The coated substrate may be rinsed in water which substantially removes the dip component of the deposited coating but does not harmfully disturb the electrodeposited coating.

A pump means 21, energized by a suitable power source (not shown), may be connected between a premix tank 22 and coating material supply means 27 by any suitable pipe conduit means 61 and 62. The premix tank 22 and the conduit means 61 and 62 may be fabricated from any suitable material which does not chemically react with coating material such as stainless steel, plastic and the like. Energization of the pump means 21 causes the pump means to supply coating material from the coating material supply means 27 to the premix tank 22 at a predetermined flow rate via conduit means 61 and 62.

A conduit means 63, which does not chemically react with the coating material, may be connected between the tank 16 and the premix tank 22 so as to permit gravity flow of coating solution 15 from the coating solution tank 16 to the premix tank 22. Alternatively, solution 15 may be intermittently withdrawn from the tank 16 and recirculated through the premix tank 22 through the conduit means 63 by means of a suitable pump (not shown).

A suitable pump 26, energized by a suitable power source (not shown), may be connected between the premix tank 22 and the solution coating tank 16 by any suitable pipe conduit means 23 and 24. The conduit means may be fabricated from any suitable material which is not chemically reactive with the coating solution. The pump 26 may be a centrifugal type pump which continuously or intermittently recirculates the coating solution in premix tank 22 to the coating solution tank 16.

A suitable agitator 25 may be used to suitably agitate the coating material contained by the premix tank 22. The agitator may be energized intermittently or continuously as desired.

Actuation of the pump means 21 by an operator based on the supposed rate of use of the coating material or the continuous replacement of the deposited coating material with coating material from the coating material supply means 27 by the pump 21 may give rise to nonaccurate control of the concentration of the constituents of the coating solution 15. Nonaccurate control of the concentration of the constituents of the coating solution may result in a less than desirable material coating film being deposited onto the substrate 10. Adjusting the concentration of the coating solution by the addition of coating material is necessary in order to obtain the proper thickness of coating material film on the substrate. Automatic replacement of the depleted coanng matenlal prior to the time the concentration of the coating material in the solution reaches a critical level would permit operation of the electrophoretic process continuously.

It was found that a more accurate control of the concentration of the constituents of the coating solution may be achieved by using an electronic device 20 connected between the cathode electrode tank 16 and the pump 21. The electronic device 20 is sensitive to the ampere-hours flowing through the coating solution. The electronic device 20 causes pump means 21 to be energized after the passage of a determined number of ampere-hours through the solution. The number of ampere-hours passing through the coating solution is proportional to the amount of coating material deposited by the coating solution per unit of time if the pH, the conductivity, the temperature, and the concentration of the coating solution are held substantially constant.

As illustrated in FIG. 2, the electronic device includes a shunt means 28 connected in series between the negative terminal of the power control unit 19 and the tank 16. The shunt means 28 may be fabricated from any suitable, low-resistance metallic material such as a strip of copper and the like. The resistance of the shunt means 28 should be such that the maximum voltage drop across the shunt means is 50 millivolts or less. The 50 millivolt drop across the shunt means 28 is proportional to the current flowing between the positively charged substrate 10 and the negative charged tank 16.

A linear amplifier 29 of the electronic device 20 is connected across the shunt means 28. A satisfactory linear amplitier is an amplifier which provides a substantially linear output signal such as Acromag Model 394 signal conditioning amplifier. The linear amplifier 29 may include a single stage isolation amplifier designed to amplify the 50 millivolt or less DC signal provided by the shunt means 28 to a 6 volt or less DC output signal.

An integrator means 30 of the electronic device 20 is connected to the output of the linear amplifier 23. The integrator means 30 converts the 6 volt or less DC output signal of the linear amplifier 29 to a pulsating output signal. The pulsating output signal of the integrator means 30 is proportional to the integral of the DC output signal provided by the linear amplifier times the length of time that the output signal is present at the output terminals of the linear amplifier 29. A satisfactory integrator means may be an Acromag reed switch integrator Model 1301. The Acromag reed switch integrator Model l30l (not shown) includes amotor, gear train, magnets and a reed switch. The output shaft of the motor rotate small magnets which actuate the reed switch. For each revolution of the shaft of the motor, two contact closures occur to provide pulses proportional to the integral of the DC signal provided by the linear amplifier 29.

A preset counter 31 of the electronic device 20 is connected to the output of the integrator means 30. The preset counter 31 may be a preset binary counter which is constructed so as to provide an output pulse when the number of input pulses from the integrator means 30 to the preset counter 31 reach a predetermined count. For example, the preset counter 31 may provide one output pulse for each 50 input pulses fed thereto by the integrator means 30.

The preset counter 31 may include a plurality of cascaded flip-flop means. An example of a single flip-flop means is shown in FIG. 3. The flip-flop means as may include a switch 41 having contact 41' connected to the positive terminal of suitable direct current source 42. The negative side of the DC source 42 is connected to point 43 through the series combination of resistor 44 and diode 45. The negative side of the DC source $2 is connected to point 46 through the series combination of resistor 47 and diode 48. Diode 49 is connected between point 46 and point 55. The coil 50 of a suitable relay is connected to a point between resistor 67 and diode 68 and to point 55. Diode 51 is connected to point 55 and to point 43. The coil 52 of a suitable relay is connected to a point between resistor 4 and diode 45 and to point 55. The first switch 52', cooperatively associated with the coil 52, is connected between point 53 and the switch ll. The second switch 52", cooperatively associated with the coil 52, is connected between point 4.6 and switch 41. The switch 50', cooperatively associated with coil 50, is connected to a point between the anodes of diodes 49 and SI and contact 4! of switch 41.

In operation of the flip-flop means 40, closure of switch 41 causes current to flow from the DC source 42 through the already closed switch 52' to point 43. Current at point 43 flows through diode 511 to point 55. It should be seen that the cathodes of diodes s9 and 51 are at substantially the same voltage level. Diode 49, however, effectively blocks the flow of current from point 55 therethrough so that current at point 55 flows through the coil 50 thereby energizing the relay closing the switch 50'. As illustrated, diode 45 is connected in parallel across the coil of relay 52 and, therefore, as long as the switch ll is closed, the relay is not energized. However, when the switch S1 is opened, the diode 45 no longer functions as a shunt across the coil 52 and the coil 52 is energized. The flip-flop means has now established a set condition. A subsequent closure of the switch 41 causes the diode 48 to function as a shunt across the coil 50 causing the switch 50' to open. The opening of the switch 50' causes point 55 to be disconnected from direct connection with the power source 42. The coil 52 continues to be energized by the current flow from the source 42 through the diode 49 until the switch 41 is subsequently opened. Subsequent opening of the switch 41 finds the coils 5i) and 52 deenergized so that the flip-flop means 49 is in the reset mode or state.

A reversible counter 32 of the electronic device 20 is connected to the output of the preset counter 31. The reversible counter counts in a first direction, that is, accumulates or adds the number of pulses fed thereto by the preset counter 31. The reversible counter 32 may be constructed so as to provide an output pulse upon an occurrence of a condition such as for example, receiving an input pulse from the preset counter 31. In the embodiment illustrated in FIG. 2, for each positive pulse present in the reversible counter 32, the reversible counter 32 provides an output pulse or an on" signal. It is recognized that the reversible counter may be constructed so as to provide an output pulse or the on" signal after the counter 32 has accumulated a predetennined number of input pulses from the preset counter 31.

A timing mechanism 33 of the electronic device 20, such as a cam timer or the like, is connected to the output of the reversible counter 32. The cam timer 33 may include a timer motor (not shown), a cam carrying shaft (not shown) and a plurality of cams (not shown) having rise and fall peripheral contours which program the operation of a plurality of follower switches (not shown) riding thereon. An output pulse or the on" signal from the reversible counter 32 causes energization of the cam timer 33 and the cam timer is caused to program a plurality of events by actuation of the follower switches (not shown). In the embodiment illustrated in FIG. 2, an energized cam timer 33 causes the pump 21 to be energized so as to provide additional coating material to tank 16 by way of the conduits 23 and 24. Also, the energized cam timer 33 causes a pulse to be provided to the reversible counter 3 which causes the reversible counter to count in a direction opposite to the direction which pulses from the preset counter 31 cause the reversible counter 32 to count. That is, the pulse caused to be emitted by the energized cam timer 32 causes the reversible counter to subtract from a positive count present thereon, if any. it is seen any combination of pulses fed to the reversible counter 32 by either the preset counter 31 or the cam timer 33 can be varied according to the dictates of the situation. In the embodiment shown in FIG. 2, it is contemplated that each pulse from the preset counter 31 fed to the reversible counter 32 causes the reversible counter to proceed into a positive state or add whereas a pulse developed on a result of energization of cam timer 33 causes the reversible counter 32 to go into a negative state or substrate. Therefore, it should be seen direction the means is deenergized causing termination of the adjusting of the coating material in the coating solution.

11. The method of claim 10, further including the step of regulating the current flow to the coating solution in response to a change in the resistivity of the coating materials deposited on the substrate 12. An apparatus for adjusting the concentration of coating materials in a coating solution, the coating materials being electrophoretically deposited upon substrates while the substrates are in the coating solution, the apparatus comprising first means monitoring a current flow from a power source to the coating solution and providing pulses substantially proportional to the integral of such current flow, pulse counter means connected to the first means and counting in a first direction in response to the pulses provided by the first means, and reversible counter means connected to the pulse counter means and to another means, the reversible counter means energizing the other means causing the coating material of the coating solution to be adjusted in response to counting of the pulse counter means in the first direction, the energized means causing counting of the reversible counter means in a second direction and when the count of the reversible counter in the second direction substantially equals the count of the reversible counter in the first direction the energized means is deenergized causing termination of the adjustment of the coating material in the coating solution.

13. The apparatus of claim 12, including means regulating the voltage to the coating solution in response to a change in the resistivity of the coating materials deposited on the substrates.

14. In combination, the apparatus of claim 12 for adjusting the concentration of coating materials in a coating solution and a tank containing the coating solution, the coating materials of the coating solution being electrophoretically deposited upon substrates while the substrates are in the coating solution.

I? i i t 

2. The apparatus of claim 1, wherein the output pulses of the first means are substantially proportional to the integral of the voltage drop with respect to time across the first means the voltage drop is present across the first means.
 3. The apparatus of claim 2, wherein the first means includes a shunt means across which the voltage drop appears.
 4. The apparatus of claim 3, wherein the first means includes an integrator connected to the shunt means, the integrator converting the voltage drop across the shunt means to the output pulses.
 5. The apparatus of claim 1, wherein the fourth means is a programming device.
 6. The apparatus of claim 5, wherein the programming device is a cam timer.
 7. The apparatus of claim 6, wherein the third means is a reversible counter.
 8. The apparatus of claim 7, wherein the second means is a preset counter.
 9. The combination of claim 1, further including conveyor means capable of causing the conductive substrates to be transported to and immersed in the electrophoretic bath.
 10. A method for adjusting the concentration of coating materials in a coating solution, the coating materials electrophoretically deposited upon an electrically conductive substrate while the substrate is immersed in the coating solution, the method comprising monitoring a current flow from a power source to the coating solution and providing pulses substantially proportional thereto, counting in a first direction in response to the pulses, and energizing a means for causing the coating material of the coating solution to be adjusted in response to counting in the first direction, the energized means causing counting in a second direction whereby when the count in the second direction substantially equals the count in the first direction the means is deenergized causing termination of the adjusting of the coating material in the coating solution.
 11. The method of claim 10, further including the step of regulating the current flow to the coating solution in response to a change in the resistivity of the coating materials deposited on the substrate.
 12. An apparatus for adjusting the concentration of coating materials in a coating solution, the coating materials being electrophoretically deposited upon substrates while the substrates are in the coating solution, the apparatus comprising first means monitoring a current flow from a power source to the coating solution and providing pulses substantially proportional to the integral of such current flow, pulse counter means connected to the first means and counting in a first direction in response to the pulses provided by the first means, and reversible counter means connected to the pulse counter means and to another means, the reversible counter means energizing the other means causing the coating material of the coating solution to be adjusted in response to counting of the pulse counter means in the first direction, the energized means causing counting of the reversible counter means in a second direction and when the count of the reversible counter in the second direction substantially equals the count of the reversible counter in the first direction the energized means is deenergized causing termination of the adjustment of the coating material in the coating solution.
 13. The apparatus of claim 12, including means regulating the voltage to the coating solution in response to a change in the resistivity of the coating materials deposited on the substrates.
 14. In combination, the apparatus of claim 12 for adjusting the concentration of coating materials in a coating solution and a tank containing the coating solution, the coating materials of the coating solution being electrophoretically deposited upon substrates while the substrates are in the coating solution. 